Volume transport of the western boundary current penetrating into a marginal sea

The amount of penetration of a western boundary current into a marginal sea which is connected to an open ocean by two narrow straits is estimated from a linear, steady and barotropic theoretical model. In this model the western boundary current in the open ocean is driven by a wind stress imposed at the sea surface. The inflow of the water of the open ocean into the marginal sea is caused by the pressure difference between two straits produced by the wind-driven circulation in the open ocean.Main external parameters are combined into two non-dimensional parameters; and (the ratio of the depth of the marginal sea to that of the open ocean), whereb is the distance between north and south boundaries of the ocean,D ₀ is the depth of the open ocean, is the latitudinal variation of the Coriolis parameter andR is the coefficient of friction. The friction is assumed to be proportional to the flow velocity.In the limit of infinite the volume transport into the marginal sea is not affected by the width of two straits and . It is mainly controlled by the wind stress and the positions of two straits. For finite values of , however, the volume transport depends considerably on and the width of the straits.Guided by both this model and physical considerations, we obtained a relation between the volume transport into the marginal sea and the external parameters. This relation predicts that about 2 % of the volume transport of the Kuroshio penetrates into the Japan Sea.     

POM and Two-Way Nesting POM Study of Kuroshio Damping Phenomenon Caused by a Strong Wind

A Kuroshio damping phenomenon of a few days scale caused by a strong wind was studied using the Princeton Ocean Model (POM) and a two-way nesting model for the POM. We simulated an idealized eastward Kuroshio in a zonal channel in terms of the inflow/outflow condition at the western/eastern boundaries and examined responses of the idealized Kuroshio to a strong easterly wind. This study was motivated by observations of JMA research vessel Shumpu Maru which reported deformation of isopycnals and damping of the Kuroshio before and after the attack of Typhoon 6804. Deformation of isopycnals and damping of the Kuroshio are found to depend on magnitude of wind stress, intensity of stratification, distance of the Kuroshio from coast, and grid resolution. The deformation of isopycnals is related to the vertical circulation pattern caused by the divergence/convergence of the onshore Ekman transport. A simple stratification model composed of Niiler (1969)'s modification of the Ekman transport and the coastal boundary is proposed to explain the damping phenomenon. An idealized cape was added in other experiments in order to study whether the Kuroshio damping mechanism discussed here works in three dimensions. The newly developed two-way nesting model for the POM was applied for this experiment and made it possible to clarify more detailed features of response in the nested area than did the coarse grid model.     

Geostrophic response near the coast

Geostrophic response of a two-layer fluid near a straight coast is investigated for a successive disturbance by the use of the inviscid, reduced gravity model. Poincare waves, coastal motion (which is trapped by the coast) and a geostrophic eddy are created. The energy of these motions is obtained. The manner in which the ocean responds is found to depend considerably on the way the disturbance is applied. When the water is supplied continuously to a calm upper layer adjacent to the coast, a quasi-steady geostrophic eddy is formed and its energy increases in proportion toT ² (T is the duration for which water is supplied). The energy of the coastal motion increases in proportion toT. When the water is supplied continuously into the upper layer from a certain portion of the coast, a geostrophic eddy is not formed. The coastal motion has the same structure as in the former case and its energy increases in proportion toT.     

Geostrophic adjustment near the coast

Geostrophic adjustment of a two-layer fluid near a straight coast is investigated for an initial pressure disturbance which has no closed geostrophic contours by using a reduced gravity (divergent barotropic) model. Propagation of a volume of water along the coast due to the internal Kelvin wave allows a non-zero solution for the final geostrophic state. Energy partitions among geostrophic motion, the internal Kelvin wave and internal Poincaré waves are obtained and compared with the result of the classical problem of geostrophic adjustment without the coast. It is found that energy partition to the geostrophic motion (EPG) with the coast is always smaller than that without the coast (EPG ), while the scale of the initial disturbance is the same. The difference betweenEPG andEPG is smaller than the energy partition to the internal Kelvin waves (EPK) and approachesEPK as the scale of the initial disturbance increases.     

Two layer model of the steady ocean response to large-scale heating and cooling

Steady response of a linear, two-layer baroclinic ocean to a steady thermal forcing was investigated on a mid-latitude -plane. Surface heat flux and its relaxation processes were parametrized as a form of heating function and Newtonian cooling term of cross interfacial velocityw in the continuity equation. Ageostrophic linear drag terms were employed to represent the western boundary layer for accomplishment of the steady circulation in the closed domain. In the interior, the dynamics belongs to thef-plane regime. The flow in the upper layer is zonal and eastward, which is the same as that expected in the channel without meridional boundary. The eastern boundary region is the so called Sverdrup region, in which the vortex stretching balances the term, thoughw contains a damping term. It directs the zonal flow southward (northward) in the south (north) followed by upwelling (downwelling) and forms the two gyres. Western boundary region is of the Stommel type except the upwelling (downwelling) in the south (north). The meridional circulation is similar to the Hadley Cell except southern and northern boundary layers. However, its strength is much greater than the latters.     

Dust in the solar system and in extra-solar planetary systems

Among the observed circumstellar dust envelopes a certain population, planetary debris disks, is ascribed to systems with optically thin dust disks and low gas content. These systems contain planetesimals and possibly planets and are believed to be systems that are most similar to our solar system in an early evolutionary stage. Planetary debris disks have been identified in large numbers by a brightness excess in the near-infrared, mid-infrared and/or submillimetre range of their stellar spectral energy distributions. In some cases, spatially resolved observations are possible and reveal complex spatial structures. Acting forces and physical processes are similar to those in the solar system dust cloud, but the observational approach is obviously quite different: overall spatial distributions for systems of different ages for the planetary debris disks, as opposed to detailed local information in the case of the solar system. Comparison with the processes of dust formation and evolution observed in the solar system therefore helps understand the planetary debris disks. In this paper, we review our present knowledge of observations, acting forces, and major physical interactions of the dust in the solar system and in similar extra-solar planetary systems.     

Use of a resistivity cone for detecting contaminated soil layers

A cone-penetration technique was developed to detect contaminated soil layers with electrolytes and NAPLs. In this study, laboratory and field experiments were performed to apply the technique. In the laboratory, the change in resistivity was quantitatively examined by adding salt or oil to soil samples. The results showed that the resistivity measurement was varied with an order of ppm for the electrolyte concentration in soil. It was found that the resistivity of sand increased with increasing oil concentration. The effect of oil content was stronger for lower water content of sand.

The results obtained from field experiments showed that the resistivity cone can be used for detecting the contaminated layer in soils whose background values are known. Particularly, the instrument can be used effectively for examining the effects of remediation, by measuring the resistivity of the ground before and after remediation, unless the soil fabric changes significantly during remediation procedures.     

Concentration mechanisms of iron oxides and alumina in deep weathering crusts (Goshikidai, Kagawa, Western Japan)

Concentration of Fe-oxides and alumina in weathering processes are main geological reactions for lateritization and bauxitization, respectively. In western Japan, red-coloured soil formed by weathering processes developed in many places. This soil is composed of hydrous Fe-oxide minerals, hydrous alumina minerals and other minerals. It was formed in the upper part of deep weathering crust by weathering processes under some kind of sub-tropical climate, probably in the Pliocene. One of these occurrences is observed in the upper part of Goshikidai and Konodai, west part of Takamatsu city, northeast Shikoku Island, west Japan. A deep weathering crust is distributed on wide hilly plains ranging from 250 to 400 m a.m.s.l. in the northwestern region of Takamatsu city. Original rock of the weathering crust is bronzite andesite and glassy bronzite andesite, so-called ‘sanukite’. The andesites had been weathered under some special climate, and the geological age of the weathering is the same as above. The mineral assemblage and formation mechanism are similar to those of laterite and bauxite. The weathering crust developing in this region are subdivided into the three following zones: (1) A zone, composed of hydrous Fe-oxides and metahalloysite with small amounts of gibbsite and it is associated with white veins of metahalloysite; (2) B zone, composed of hydrous Fe-oxides and metahalloysite (some material is associated with -cristobalite); and C zone, composed of metahalloysite or halloysite and -cristobalite with relict crystals of feldspar and quartz, and some material is associated with montmorillonite. Chemical analyses of the materials of the three zones show the formation mechanisms of the weathering crust.     

Importance of Reference Dataset Improvements for Argo Delayed-Mode Quality Control

For the Argo Project, monitoring the global upper ocean by a large number of profiling floats, maintaining the quality of salinity data is critical; the goal for measurement accuracy is ±0.01. Experiments using the method of Wong et al. (2003), the standard delayed-mode quality control (dQC) for the Project, show that its performance depends critically on the reference datasets used. This study concludes that the method is useful for Argo and has sufficient potential to achieve the goal for salinity measurement in the North Pacific, when suitable reference datasets are prepared. Considering the Wong et al. (2003) algorithms, we suggest that reference datasets with the following characteristics will be most suitable for Argo dQC: They should be basically derived from the most extensive datasets, such as the latest World Ocean Database; in regions with denser observations, datasets with carefully quality controls should be used; in the regions with subsurface temperature inversions, such as the subarctic North Pacific, the profiles used for the reference must extend below the deepest temperature maximum to prepare proper salinities for the deep layer reference.     

Application of microtremor measurements to the estimation of earthquake ground motions in Kushiro city during the Kushiro-Oki earthquake of 15 january 1993

Microtremor measurements were conducted in Kushiro City, Hokkaido Island of Japan. The thickness of alluvial deposits in the central area of Kushiro City abruptly changes from 0 to 80 m. Predominant ground motion at a microtremor measuring site is represented by the spectral ratio, the ratio of Fourier amplitude spectrum of microtremor in the horizontal direction to that in the vertical direction. The peak frequency of the spectral ratio corresponds well to the predominant frequency estimated from the thickness of alluvial layer at each site. Based on a hypothesis that the spectral ratio can be regarded identical with a half of the amplification factor from diluvial bed rock to the ground surface, the strong ground motion due to the Kushiro-oki earthquake at each site is estimated. The method of estimation is verified by the comparison of the synthesized accelerogram with the recorded one at West Port of Kushiro. The results satisfactorily explain major damages and vibrations felt in Kushiro City during the earthquake.